1. Field of the Invention
This invention relates to analog-to-digital conversion apparatus, and more particularly, to an analog-to-digital converter having unipolar current and voltage conversion modes of opposite polarity adapted to perform bipolar current and voltage analog-to-digital conversions.
2. Background Information
Commonly owned U.S. patent applications Ser. No. 07/470,471, filed on Jan. 26, 1990 entitled "SuRE Chip" discloses an integrated circuit (IC) and more particularly, a complimentary metal oxide semiconductor (CMOS) IC which includes an on board microprocessor, and analog-to-digital (A/D) subsystem, and various input/output devices on a single monolithic chip for use in various types of electrical equipment, such as circuit breakers, motor controllers, contactors and the like for converting analog signals, such as electrical voltages and currents, to digital signals for monitoring and control. This IC has several analog input channels which are capable of performing analog-to-digital conversions on either currents or voltages. However, it is only capable of performing conversions on negative currents and positive voltages. There are several applications of the SuRE Chip which require A/D conversions of signals which have both positive and negative values at different times. To date, this has required additional circuitry to process the bipolar signals. For instance, a full wave rectifier and a comparator providing a polarity bit have been used for this purpose.
There is a need for a simpler, less expensive arrangement for adapting the A/D subsystem of the IC to make bipolar A/D conversions.